Project Summary Electrical stimulation of primary visual cortex (V1) via implanted microelectrode arrays has been proposed as a means to restore vision to those suffering from a wide range of visual impairments. Despite some initial clinical success, systematic advances have been limited by an inability of such devices to selectively target specific neuronal sub-populations as well as by the foreign body responses and other reactions that can compromise the long-term efficacy of implants. Our goal here is to enhance the efficacy and the reliability of cortical implants by developing a micro-coil array for intracortical magnetic stimulation. Coil-based magnetic stimulation has several important advantages when compared to electrode-based electric stimulation. First, the electric fields induced by the coils are spatially asymmetric and can therefore be used to selectively activate vertical pyramidal neurons in the cortex without also activating the horizontal passing axons of other cortical areas, thereby enhancing the spatial resolution of cortical stimulation. Second, the magnetic fields arising from the coils have high permeability to any biological tissue and so they can pass readily through the high impedance glial scarring that encapsulates cortical implants and thus continue to reliably induce electric fields in the targeted area. Third, the micro-coil array can be made more reliable by hermetically sealing the entire device with dielectric coatings so that it will not be plagued by the device degradation caused by water infiltration through the weak bonding between the exposed electrode and the dielectric coating and/or delamination of the thin metal electrode from the substrate during chronic stimulation. Thus, the coil-based approach provides a more effective and more reliable approach for neural stimulation with cortical prostheses. The aims of this proposal are to further enhance the efficacy and reliability of visual prosthetics by optimizing the design of a micro-coil array, developing more effective stimulation strategies, and establishing efficacy in mice that are blind due to retinal degeneration (rd10).